Facsimile transmission in a digital cellular radio network

ABSTRACT

A facsimile service arrangement in a digital cellular radio network including radio terminal equipment; data terminal equipment which is connected to the radio terminal equipment and is the source or destination of fax messages to be transmitted; a fax device with a 2-wire line interface and a control interface, to which the data terminal equipment is operationally connected to control the fax device; a network terminating unit disposed in a mobile exchange; and call control means for establishing a digital data transmission connection between the network terminating unit and the radio terminal equipment. The fax device is a fax modem disposed in the network terminating unit, and the data terminal equipment is operationally connected to the control interface of the fax modem through the radio terminal equipment and the digital data transmission connection.

FIELD OF THE INVENTION

The invention relates to a facsimile service in a digital cellular radionetwork.

BACKGROUND OF THE INVENTION

In connection with the standardization of the European mobile phonesystem GSM plans have been made to include a facsimile service in thesystem with equipment configuration as shown in FIG. 1. The presentfacsimile terminals employ a modem interface and a 2-wire connection(modem connection), for example, via a telephone network. Thus, allsignalling between fax terminals has taken place over a modemconnection. In a digital cellular radio network at least one of the faxterminals would be disposed in connection with a mobile radio unit,whereby the fax connection must be established through a radio linkbetween the mobile radio unit and the fixed network. In the GSM cellularradio system, this has been planned to be embodied in accordance withFIG. 1: a fax terminal 1 is connected in a normal manner over a 2-wiremodem connection to a specific fax adaptor 2, by means of which thesignals of the 2-wire connection are adapted to a specific dataconnection established over the radio link between the mobile radio unitMS and the base station system BSS to a mobile exchange MSC and furtherto a network terminating unit IWF comprising a second fax adaptor 5. Thesecond fax adaptor 5 adapts the above-mentioned data connection to aconventional 2-wire modem connection, for example, through a publicswitched telephone network PSTN to another fax terminal. Theimplementation of a fax connection over a radio path involves, however,different kinds of problems, wherefore the standardization of thefacsimile service according to FIG. 1 is still unaccomplished, and thefacsimile service will not be available for the GSM users for some time.

SUMMARY OF THE INVENTION

An object of the present invention is to render facsimile transmissionpossible in the present digital cellular radio systems.

According to the invention, an arrangement for facsimile transmission ina digital cellular radio network, this arrangement comprising radioterminal equipment; data terminal equipment which is connected to theradio terminal equipment and is the source or destination of faxmessages to be transmitted; a fax device with a line interface for a faxconnection and a control interface, to which the data terminal equipmentis operationally connected to control the fax device; a networkterminating unit in a mobile exchange; and call control means forestablishing a digital data transmission connection between the networkterminating unit and the radio terminal equipment, is characterized inthat the fax device is a fax modem disposed in the network terminatingunit, and that the data terminal equipment is operationally connected tothe control interface of the fax device through the radio terminalequipment and said digital data transmission connection.

The idea of the invention is to dispose a fax modem in a networkterminating unit in association with a mobile exchange so that a dataterminal in association with the radio unit controls the fax modemthrough a standard data connection established between the networkterminating unit and the radio unit. In other words, the data terminal,e.g. a personal computer PC, controls the fax modem as if it wereconnected directly to the data terminal via a standard control interfaceexcept that in the invention the standard interface is "extended" overthe data connection through the cellular radio network. The inventionallows the fax modem to be a commercially available fax terminal and thedata terminal to be e.g., a conventional personal computer PC providedwith software for such transmission carried out through the fax modem.By means of the invention it is possible to avoid system-specific faxadaptors at both ends of the data connection, whereas in theconfiguration under standardization they are necessary. Thus, theinvention renders it possible to implement a facsimile service veryadvantageously even with the existing commercial equipment and by theuse of existing data transmission facilities of a cellular radiotelephone.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail by means of illustrativeembodiments with reference to the accompanying drawings, in which:

FIG. 1 is a block diagram which illustrates the system configuration forfacsimile transmission as intended to be implemented according to theGSM recommendations,

FIG. 2 is a block diagram which illustrates the system configuration forfacsimile transmission according to the invention,

FIG. 3 is a block diagram which illustrates the structure of a cellularradio system,

FIG. 4 is a block diagram which illustrates the structure of a mobilestation and the connection of a data terminal thereto, and

FIG. 5 is a block diagram which illustrates a mobile exchangeimplemented according to the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

The fax transmission concept according to the present invention isapplicable to any digital cellular radio system. It is particularlysuitable for use in the European digital mobile telephone system GSM andcorresponding digital systems, such as DCS1800 and PCN (PersonalCommunication Network). In the following, the preferred embodiment ofthe invention will be described in connection with the GSM system; itis, however, not restricted to this system.

FIG. 3 is a schematic view of part of the GSM cellular radio system. Ina cellular radio system the area covered by the system is divided intoradio cells. Two base station controllers BSC1 and BSC2 are connected toa mobile exchange MSC by digital transmission connections 12. Basestations BTS1, BTS2 and correspondingly BTS3 and BTS4 are furtherconnected to the base station controllers BSC1 and BSC2 by digitaltransmission connections 11. Each BSC and the base stations associatedwith it form a base station system BSS. Typically the radio coveragearea of a base station BTS forms a radio cell. Each base stationBTS1-BTS4 has a predetermined number of physical radio channels. Asignal (physical channel) of the GSM system consists of TDMA frames,each of which contains preferably eight time slots used as logicalchannels. The logical channels contain traffic channels for calls (voiceand data) to be set up with mobile stations MS located within the cell,and control channels for signalling performed with the mobile stationslocated within the cell. Over the traffic channels it is possible toestablish a speech connection, a V.110 rate-adjusted 64 kbit/sfull-duplex data connection or a 9.6/4.8/2.4 kbit/s data connection. Theinvention can, however, be applied to any digital transmission channel.Special purpose adaptors are typically required at both ends of the dataconnection for adapting the data connection to terminal equipment and/orother transmission connections/systems. The adaptor connected to theterminal equipment is usually called a terminal adaptor, and the adaptorat the network end a network adaptor. In the GSM mobile phone systemsuch a network adaptor is located in a mobile exchange MSC.

According to the invention, a facsimile service for a mobile station MScan be provided in a cellular radio system by disposing a fax modem FAXin a network adaptor IWF of a mobile exchange MSC. A data terminal 21(DTE) connected to the mobile station MS can thus control the fax modemthrough a data connection which is established on a logical trafficchannel from the mobile station MS to the MSC by means of the radio linkbetween the MS and the base station system BSS. The control interface ofthe fax modem FAX is connected to said data connection, and the lineinterface (modem interface) is connected to a normal telephone or modemconnection (2w), at the other end of which there is another conventionalfax terminal equipment 10, which may be connected e.g. to a publicswitched telephone network 9 (PSTN).

The fax modem FAX in the network adaptor IWF can be any suitable modemintended for fax transmission, e.g. a fax modem of the type Class1 orClass2. Class1 and Class2 are EIA standard proposals and de factoindustrial standards specifying the protocol for an asynchronousinterface between fax modems and the software using them. The differencebetween these two classes is that a Class1 modem attends only to thephysical and data connection layer of a fax session, whereas a Class2modem also deals with T.30 fax session management (and leaves thus lessresponsibility for the software). Normally when Class1/Class2 fax modemsare used, the physical link between the computer PC and the fax modem isa serial cable, e.g. RS-232. In the invention this serial connection isextended as an asynchronous data connection through the cellular radiosystem.

FIG. 4 shows a mobile station MS and data terminal equipment DTEconnected thereto. The MS 33 comprises a radio unit 36, call control 39,a user interface 40 (e.g. keyboard and display), mobility management 41,radio path management (signalling functions) 42, and a terminal adaptor37 providing a V.24 interface. The radio unit 36 comprises e.g., a radiotransceiver connected to an antenna 55, and a channel coding anddecoding unit 43. By means of a two-way switch unit 38, the unit 43 canbe connected either to a telephone unit, comprising e.g. a speech codec56 and a telephone receiver 34, or to a terminal adaptor 37.

The terminal adaptor 37 comprises a unit 46 which performs adaption forthe GSM data connection. The unit 46 is connected to the two-way switch38 via an I/O circuit 45 and to a data terminal 31 via an I/O circuit47, which forms the interface 53 (e.g. V.24).

FIG. 5 illustrates one way of applying the invention to a mobileexchange MSC. For the sake of clarity, FIG. 5 shows only the switchingfield 83 and call control 82 included in the exchange, but in practicean MSC contains a large number of various devices. The switching field83 may be an analog or digital switching device which selectivelyconnects speech and data connections between transmission lines 12 fromthe base station system BSS and transmission lines 13 from a mobileexchange. An example of such digital telephone exchanges is Telenokia DX220 MSC.

A network adaptor 80A (IWF) is connected in parallel with the switchingfield 83 in such a manner that the signal port P1 of the network adaptoris connected to the port O_(N-1) of the switching field 83, and thesignal port P2 is connected to the port I_(N-1) on the opposite side ofthe switching field 83. Another network adaptor 80B (or more) can beconnected correspondingly in parallel with the switching field 83. Thenetwork adaptor 80 comprises a data transmission service adaptor DASAclose to the port P1, said adaptor adapting the GSM data connection tothe V.24 interface 81. The control interface of a fax modem FAX isconnected to the V.24 interface 81, and the line or modem interface ofthe fax modem FAX is connected to port P2 of the network adaptor 80. Inthe following, the operation of the fax arrangement according to theinvention will be described so that mobile originated and mobileterminated Galls will be dealt with separately.

As the fax modem FAX disposed in the network adaptor 80 is not astandard facility of the GSM system, a special way must be developed foraddressing it from the MS. In one embodiment of the invention, adedicated telephone number is reserved for the facsimile service; callsmade to this number are routed automatically to the network adaptor 80of the MSC. When the MS wishes to send a fax, it initiates the faxtransmission by making a call to this fax service number. The MSC routesthe call to the network adaptor 80 by connecting line 12 to port P1 ofthe network adaptor 80A, and by connecting port P2 to another outgoingline 13, as illustrated by a broken line in FIG. 5. After theestablishment of a data connection between a terminal adaptor 37 and thenetwork adaptor 80A, an indication of the completed connectionestablishment is sent to the MS e.g. in the form a CONNECT call controlmessage. The DTE issues suitable Class1/Class2 and AT commands over thedata connection to a fax modem FAX, which dials the number of thereceiving fax terminal 10 and establishes a modem connection with it.Once the fax session has been started, the DTE controls the fax modemFAX as if they were connected directly to each other. When the faxsession is to be terminated, the DTE gives a termination command to thefax modem FAX, whereafter the MS disconnects the GSM call in the normalway.

An alternative way of establishing the data connection is to use theBearer Capability element of a GSM call set-up message in a non-standardway: for example, by setting the modem type field to an undefined value.

A mobile terminated call is somewhat more difficult. If fax connectionsare also desired for mobile terminated calls, another service number maybe used for example as follows. The MSC has a service number which isdedicated for incoming fax calls to the MS. A user (e.g. subscriber of apublic switched telephone network PSTN) who wants to send a fax to amobile station MS can manually dial this number. This call may at firstbe directed, for example, to the call control 82 of the MSC. When theservice number replies, the user presses the transmission button in hisfax machine, whereby the fax machine transmits the number of thesubscriber station MS as DTMF (Dual Tone Multi Frequency) tone codes.The MSC decodes these DTMF tone codes and starts call set-up with saidMS. When a data connection has been established, the MSC connects thedata connection in the manner described above to the fax modem FAX andconnects the link on line 13, coming from the PSTN, from the fax machine10 to port P2 of the network adaptor 80A. When the fax modem FAX of thenetwork adaptor 80A observes that the fax machine 10 is calling itthrough the modem connection, it outputs a RING message from a serialcontrol interface 81. This message is transmitted over the GSM dataconnection to a serial port 53 of the data terminal 21, and, as aresponse, the data terminal sends a reply command to the fax modem.Thereafter the fax session continues in accordance with a normalClass1/Class2 case except that the data terminal must again control theMS to disconnect the GSM radio link after the fax session is terminated.

The DTE 21 may be, for example, a conventional personal computer PC,such as MikroMikko 4TT m326, with suitable fax communication software,such as WINFAX. The fax modem FAX may be, for example, Headlink 24 FAX,which is a fax modem of the type Class2. The other fax machine 10 may beany standard fax machine. The transmission rate of the GSM dataconnection is preferably 9600 bit/s.

The settings of the control interface (W.24) of the fax modem FAX maybe, for example, as follows: line speed 4800 bit/s; error correctionLAPM; terminal speed 9600 bit/s; flow control (off), and V.24 controllines as follows: 108.1 and RTS are ignored, and DSR, DCD and CTS arealways on. The selected line speed of the fax modem FAX may also be 9600bit/s, but in that case suitable compression, such as V.42 bis, must beused in the fax transmission.

The figures and the associated description are intended merely toillustrate the present invention. The details of the present inventionmay vary within the scope and spirit of the attached claims.

I claim:
 1. An arrangement for facsimile transmission in a digitalcellular radio network, said arrangement comprising:radio terminalequipment; data terminal equipment which is connected to the radioterminal equipment and is the source or destination of fax messages tobe transmitted; a fax device with a line interface for a fax connectionand a control interface, to which the data terminal equipment isoperationally connected to control the fax device; a network terminatingunit in a mobile exchange; and call control means for establishing adigital data transmission connection between the network terminatingunit and the radio terminal equipment; the fax device being a fax modemdisposed in the network terminating unit; and the data terminalequipment being operationally connected to the control interface of thefax device through the radio terminal equipment and said digital datatransmission connection.
 2. The arrangement according to claim 1,wherein:in the case of an outgoing fax call, the radio terminalequipment initiates the fax call by instructing the call control meansto establish said data transmission connection, whereafter the dataterminal equipment starts a fax session through the radio terminalequipment, the data transmission connection and the fax device withanother fax device at the other end of the fax connection.
 3. Thearrangement according to claim 1, wherein:in the case of an outgoing faxcall, the radio terminal equipment initiates the fax call by dialling apredetermined service number, which results in the establishment of saiddata transmission connection, whereafter the data terminal equipmentstarts a fax session through the radio terminal equipment, the datatransmission connection and the fax device with another fax device atthe other end of the fax connection.
 4. The arrangement according toclaim 1, wherein:the call control means are responsive to incoming faxcall so as to initiate the establishment of said data transmissionconnection, whereafter the data terminal equipment starts a fax sessionthrough the radio terminal equipment, the data transmission connectionand the fax device with another fax device at the other end of the faxconnection.
 5. The arrangement according to claim 4, wherein:theestablishment of the data transmission connection is initiated bydialing a predetermined service number and transmitting the number ofthe called radio terminal equipment.
 6. The arrangement according toclaim 2, wherein:the fax connection between the fax device and saidother fax device is a connection in a public switched telephone network.7. The arrangement according to claim 1, wherein:the control interfaceof the fax device is in compliance with EIA Recommendation Class 1 orClass
 2. 8. The arrangement according to claim 1, wherein:the controlinterface of the fax device and the data terminal is a serial interface,the signals of which are transferred over said data transmissionconnection transparently or non-transparently.
 9. The arrangementaccording to claim 8, wherein:said serial interface is an RS-232 serialinterface.